Abstract
Abstract Shear-driven kinetic Alfven waves (KAWs) at the plasma sheet boundary layer (PSBL) were investigated for substorm events in the presence of a parallel electric field using the general loss-cone distribution function. Using a kinetic approach, we derived the expressions for dispersion relation and growth length of the KAW in the presence of the parallel electric field using the general loss-cone distribution function for both, weak and strong shear regimes. The frequency of the KAW obtained is in agreement with observed values of 0.1–4 Hz in the PSBL. The results explain the generation of the energetic KAWs at the PSBL by the shear at substorm onset. The parallel electric field associated with the energetic KAWs at substorm onset may heat the field-aligned electrons, leading to parallel electron energisation that ultimately causes an intense aurora. The electric field along magnetic field lines enhances the frequency of KAW but decreases the growth length in the case of weak shear. We also found that the parallel electric field can reflect KAW towards the PSBL. The loss-cone distribution index changes the profiles of frequency and growth length plots of the shear-driven KAW. Hence, the loss-cone distribution function is an important factor in the excitation of KAW in the active region of the magnetosphere, such as the PSBL and the auroral acceleration region.
Highlights
A magnetic substorm is a transient process that leads to a reconfiguration of the magnetotail
We derived the expressions for dispersion relation and growth length of the kinetic Alfven waves (KAWs) in the presence of the parallel electric field using the general loss-cone distribution function for both, weak and strong shear regimes
We found that the parallel electric field can reflect KAW towards the plasma sheet boundary layer (PSBL)
Summary
A magnetic substorm is a transient process that leads to a reconfiguration of the magnetotail. The Polar satellite has observed dominant parallel electric field signatures with amplitudes of up to 150 mV/m that were associated with the large-amplitude Alfven waves in the PSBL during the sustorms (Wygant et al, 2000; Keiling et al, 2005) Both observations and global magnetohydrodynamic (MHD) simulations have revealed that velocity shear can build up in the magnetosphere due to solar wind compression (Gavrishchaka et al, 1996). The purpose of our study was to study the shear-driven KAW in the presence of the parallel electric field using the loss-cone distribution function within the framework of simultaneous observations at the substorm-related KAWs in the PSBL, downward flowing electrons and upward flowing ions.
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